Apparatus for dimpling sheet metal stock



NOV; 16, 1948. V SCHWARTZ 2,453,762

APPARATUS FOR DIMPLING SHEET METAL STOCK Filed Jan. 27, 1945 2 Sheets-Sheet 1 INVENTOR ARTHUR A. SCHWARTZ M0 @u-ATTORNEYS Nov. 16, 1948. A. A. SCHWARTZ 2,453,762 I APPARATUS FOR DIMPLING SHEET METAL STQCK Filed Jan 27, 1945 2 Sheets-Sheet 2 28 V INVENTOR ARTHUR A. SCHWART a M, ATTORNEYS Patented Nov. 16, 1948 APPARATUS. FOR mivirnmessneer METAL STOCK Arthur A. Schwartz, Bufialo fN l YL, assigncr itn. Bell Aircraft Corporation;:BuffalMNX.

Applicationlanuary 2'7, 1945,,Seiial No. 574,862,

(Cl. .1 53-'--321JJ).

2 Claims.

This invention relates to a machining means such as is adapted to metal pressing and like operations, and more particularly to an improved means for locally dimpling sheet metal stock pieces and the like as in connection with large manufacturing operations.

One of the objects of the invention is to provide an improved means for dimpling or pressing shop stock pieces into reformed shapes. Another object of the invention is to provide an improved dimpling means such as is adapted particularly to provide improved results in connection with rapid multiple pressing operations. Another object of the invention is to provide an improved means for dimpling thermoplastic stock pieces, such as is particularlysuitable for example to provide multiple local deforming operations at rapid rate.

Another more specific object of the invention is to provide an improved die type mechanism for locally dimpling cold sheet metal stock pieces and the like into reformed shapes. Another object of the invention is to provide an improved method and means for dimpling sheet metal stock pieces at rapid rate while reducing the stock material fracturing tendencies. Another more specific object of the invention is to provide an improved method and means for dimpling stock of normally nonmalleable metal such as aluminumand magnesium alloy stock sheets and the like. Other objects and advantages of the invention will appear in the specification hereinafter.

In the drawings;

Fig. 1 is a fragmentary general arrangement View of anapparatus of the invention; and

Fig. 2 is a fragmentar vertical. section, on .an enlarged scale, through thediezportions of the apparatus of Fig. 1 showing a work sheet in operative positionthereon.

The drawing illustrates a so-called dimpling process being applied to a work sheet. designated generally at H); the work sheet having been previously drilled as indicated at l2--l2|.2. so as to receive rivets :or the like as in. connection for example with fabrication of sheet metal skin parts for aircraft or the like. The invention is shown as being applied to the drilled work sheet It! for the purpose of locally dimpling the work sheet at the region of each of the drilled holes so as to form a countersink thereat. Such-operations are more commonly known as dimpling, and will adapt the work sheet to receive the conically shaped heads of rivets or the like when inserted through the openings .lf2- l-2-l 2 insuchmanner that the rivet-heads will bra-disposed flush with the'bottom surface of -thework sheet I O as shown in "Fig.2.

"In certain arts as for examplein the aircraft manufacturingartylarge quantities of multiple drilled-and'countersunkwork sheets ofthe character of the'work sheet In ofthe drawing are required; and such work sheets are often formed of special alloys designed toprovide such sheets to-be extremely light weight yet of sufiicient strength and rigidity to successfully withstand the loads to-be-imposed thereon. Suitable alloys for such purposes usually-inciudethe aluminum and magnesium-type alloys'such as are relatively nonmallea-ble atnormal temperatures. Therefore, it 'is clifliculttodimple such work sheets when in cold condition without fracturing and tearing thestock material in the region of each dimpling operation. Yet it isundesirable to overall heat such worksheets prior to such di-mpling opera-- "time because such overall heating renders the work sheets 'relatively soft and unstableand subject to twisting andwrinkling distortions-during the handling operations incidental to transferring themf-rom the heating operation tothedimpling 1 operation. Also, such overall heating methods are undesirable because of the additional step involved therebyand' the extra facilities required to perform-such operations, and theextra time and expense incidental thereto.

The present invention'obvi'ates the objections and disadvantages referred tohereinabove by providing the-work sheet lio=be spontaneously heated only locally exactly at theregions'of the dim-pling operations; the-heat'beingthereby focalized upon only the portion-or portions ofthe sheet required "to be heated,-so as torbring such portions rapidly :tothe optimum=temperature for the dimpling operations while avoiding: overallweakening of the work sheet structure.

Withthe above purposes in'view the apparatus of 'tlie invention may comprise, as illustrated in the dravving, an-upperdie l B andza punch member 24- arranged in opposing relation to receive "the 'work sheet to ibe dimpled therebetween. Any suitable means for "providing relative movement between: the die teand' the punch member 24 maybe employed, butvas illustrate-ed in the drawing'-the-*upperldielli may be carried by a ram stem 20-so as'to be adapted to be alternately pushe'd 'and =pull'ed toward and away from the punchmemberfl. A supporting member 18 located beneath the upper die 11 6 is centrally bored are Z andslidably mounted upon the punch mem- "beri 'I his punch'member extends from a stationarybase'-p1ate "26l having ath-reade'dstub-portion 28 for convenient mounting upon any suitable stationary base device. A compression spring 30 is arranged between the base plate 26 and the supporting member I8 so as to normally maintain this member in spaced relation from the base plate 26 as illustrated in Fig.2.

The punch member 24 carries integrally therewith a pilot boss 32 extending therefrom such as is adapted to be inserted through the openings drilled through the work sheet preliminary to performance of the "dimpling operation, where'- by each drilled portion of the work sheet will be automatically centrallized relative to the punch member 24 when mounted upon the pilot boss 32. The upper end of the punch member 24 is conically shaped as indicated at 34 and the upper die it is bored as indicated at 36 to receive the boss 32 and is counterbored as indicated at 38 to complement the shape of the conical mandrel portion 34. Thus, it will be understood that upon application of power to the ram 20 the upper die IE will be forced so as to first contact the upper surface of the work sheet l6 and then to depress-the latter along with the supporting member I8 against the action of the spring 30. Since the punch member 24 is stationary the conically surfaced portion 3 thereof is thereby forced to press the material of the stock piece surrounding the aperture 12 upwardly into the countersink portion 38 of the upper die I6; thereby formingthe material of the stock piece into the shape indicated at ll! in the region of the opening l2 at the right hand side of the stock piece it). Stop blocks 42 42 may be provided to extend from the base plate 26 to limit the retrograde movement of the-supporting member l8, as may be desired.

To provide local malleabilizing of the stock piece such as is required to prevent fracturing thereof in connection with each dimpling operation, the upper die l6 and the supporting member is are each provided with heat supply means. This may be in the form of conduits 4446 extending gas shown through the interior of the die It and supporting member la in such manner as to encircle the stock piece shaping portion of the die It and the punch member 24 while being in relatively close proximity thereto; and means are provided for circulating a heating fluid medium through the channels i l-46.

For example, as illustrated in Fig. 2, the conduits 44-45 may be provided in the die and supporting member bodies by first externally grooving the latter and then enclosing the grooved surfaces thereof by means of metallic sleeves 48-48 which may be sweated or otherwise mounted thereon in fluid leak-proof manner. Heat insulating sheathes 56-56 of asbestos or the like may be wrapped about the sheathes 48-48, and heating fluid inlet-outlet conduits 52-54 are connected in open communication with the corresponding channeled portions 44-46. The conduits 54-54 lead from a single heated fluid supply manifold '55 (Fig. l), and the conduits 52--52 lead to a common fluid discharge manifold 56. Heating elements such as illustrated at 58-58 may be arranged in conjunction with the hot fluid manifold 55, and may comprise any suitable heating devices such as electrical heating means controlled by rheostats as indicated at 60-60. The manifold is illustrated as being arranged to be fed with a supply of compressed air at 62, and the air discharge conduit 56 may be returned as indicated at 64 into open communication with a jacket 65 surrounding a portion of the compressed air conduit 55 for preheating the latter,

thus effecting substantial saving in the operation required of the heating elements 58-58. The hot air jacket 65 exhausts into the atmosphere as at 66.

Thus, it will-be understood that immediately upon mounting the stock piece in operative position upon the supporting member l8 the heat emanating therefrom will permeate the stock piece in the immediate region of contact with the punch member where the dimpling operation is commenced. Similarly, upon initial contact of the heated upper die [6 with the stock piece, a heat transfer operation in the stock piece will be set up in the immediate region where the dim pling operation is to be performed. Then as the die jaws squeeze down upon the stock sheet the dimpling operation will be accompanied by further heat transfer effects such as will bring that portion of the stock piece which is being forged to the desired malleabilizing temperature. Thus, a particular feature and advantage of the invention is that each local heating operation is performed automatically without attention by the operator and in exact synchronism with each 10- cal dimpling process, whereby the work sheet may be momentarily brought up to optimum forging temperature Without requiring an undesirable elongation of the maximum heating period,

I have determined that heated air may be used with particular advantage for the die heating medium as illustrated and described hereinabove whenever the stock pieces being fabricated are of relatively thin sheet and rapid heat transfer form. It seems that the use of hot air for this purpose makes it possible to provide extremely flexible temperature control such as to almost spontaneously procure optimum dimpling temperatures at the areas to be forged while avoiding producing annealing temperature conditions in the stock sheets such as would adversely affeet the stock sheets for the purposes for which they are intended.

Although only one application of the method of the invention and only one form of the apparatus thereof have been illustrated and discussed in detail, it will be understood that the invention is also applicable to various other manufacturing operations and that various changes may be made in the apparatus as disclosed herein without de parting from the spirit of the invention or the scope of the appended claims.

I claim:

1. An apparatus for dimpling preperforated sheet metal stock, comprising an upper die formed with a counte-rbore and an associated countersunk. portion, a punch member having a pilot for successive engagement with the apertures of the stock, said punch member also having a conically surfaced portion for cooperation with the countersunk portion of the upper die, means for moving said die and said punch member toward each other to perform a dimpling operation on the interpo-sed stock around the engaged aperture thereof, a workpiece supporting member slidably carried by said punch member, said upper die and said supporting member each being formed with an external annular groove, an annular metallic sleevepermanently secured to said upper die, an annular metallic sleeve permanently secured to said member, said sleeves serving to enclose the annular grooves in said die and said member to form circulating channels for heated compressed air, an inlet conduit and an outlet conduit carried by said upper die and said memher for conducting heating medium to the grooves thereof, an inlet manifold connecting said inlet conduits, an outlet manifold connecting said outlet conduits, means for heating compressed air supplied to said inlet manifold, and a jacket connected to said outlet manifold, said inlet manifold passing through said jacket to preheat the air supplied to the heating means.

2. An apparatus for dimpling sheet metal stock,

comprising a die formed with a countersunk portion, a punch member having a conically sur- 1 faced portion for cooperation with the countersunk portion of the die, means for moving said die and said punch member toward each other to perform a dimpling operation on the interposed stock, a workpiece supporting member slidably carried by said pun-ch member, said die and said supporting member each being formed with an external annular groove, an annular metallic sleeve permanently secured to said die, an annular metallic sleeve permanently secured to said member, said sleeves serving to enclose the annular grooves in said die and said member to form circulating channels for heated compressed air, an inlet conduit and an outlet conduit carried by said die and said member for conducting heating medium to the grooves thereof, an inlet manifold connecting said inlet conduits, an outlet manifold connecting said outlet conduits, an outlet manifold connecting said outlet conduits, means for heating com-pressed air supplied to 6 said inlet manifold, and a jacket connected to said outlet manifold, said inlet manifold passing through said jacket to preheat the air supplied to the heating means.

ARTHUR A. SCHWARTZ.

REFERENCES CITED The following references are of record in the O file of this patent:

UNITED STATES PATENTS OTHER REFERENCES The disclosure on p. 25 of the Journal of Aeronautical Sciences, vol. 18, No. 1, Nov. 1940. (A copy of this disclosure can be found in Class 153 subclass 21A in Division 14 of the Patent Oflice.) 

